Biosensor with predetermined dose response curve and method of manufacturing

ABSTRACT

The present invention provides a system of biosensors whose dose-response curves are maintained within a predetermined and desired range or tolerance during production by selecting a feature of the biosensors that can be varied during production. For example, in one exemplary embodiment the effective area of the working electrode of an electrochemical biosensor can be varied during production as needed to offset variations that occur, e.g., in the reagent of the biosensors as production proceeds. In another exemplary embodiment, the dose-response curve of biosensors not yet produced can be predicted and one or more features of these biosensors can be selected to maintain the dose-response curve within a predetermined range or tolerance.

BACKGROUND

The present invention relates to biosensors for use in measuringconcentration of analytes in biological fluids, and more particularly,to variations in the dose-response curves of such biosensors that occurduring production.

Measuring the concentration of substances in biological fluids isimportant for diagnosis and treatment of many medical conditions. Forexample, the measurement of glucose in body fluids, such as blood, iscrucial to the effective treatment of diabetes. Multiple methods areknown for determining the concentration of analytes in a blood sampleand generally fall into one of two categories: optical methods andelectrochemical methods.

Optical methods generally involve spectroscopy to observe the spectrumshift in the fluid caused by concentration of the analyte, typically inconjunction with a reagent that produces a known color when combinedwith the analyte.

Electrochemical methods generally rely upon the correlation between acurrent (amperometry), a potential (potentiometry) or accumulated charge(coulometry) and the concentration of the analyte, typically inconjunction with a reagent that produces charge-carriers when combinedwith the analyte. See, for example, U.S. Pat. No. 4,233,029 to Columbus,U.S. Pat. No. 4,225,410 to Pace, U.S. Pat. No. 4,323,536 to Columbus,U.S. Pat. No. 4,008,448 to Muggli, U.S. Pat. No. 4,654,197 to Lilja etal., U.S. Pat. No. 5,108,564 to Szuminsky et al., U.S. Pat. No.5,120,420 to Nankai et al., U.S. Pat. No. 5,128,015 to Szuminsky et al.,U.S. Pat. No. 5,243,516 to White, U.S. Pat. No. 5,437,999 to Diebold etal., U.S. Pat. No. 5,288,636 to Pollmann et al., U.S. Pat. No. 5,628,890to Carter et al., U.S. Pat. No. 5,682,884 to Hill et al., U.S. Pat. No.5,727,548 to Hill et al., U.S. Pat. No. 5,997,817 to Crismore et al.,U.S. Pat. No. 6,004,441 to Fujiwara et al., U.S. Pat. No. 4,919,770 toPriedel, et al., and U.S. Pat. No. 6,054,039 to Shieh, which are herebyincorporated in their entireties.

Electrochemical biosensors for conducting tests are typically providedas a disposable test strip having a reagent thereon that chemicallyreacts with the analyte of interest in the biological fluid. The teststrip is mated to a test meter such that the test meter can measure thereaction between the analyte and the reagent in order to determine anddisplay the concentration of the analyte to the user.

The response of an electrochemical biosensor to a potential step islargely governed by the Cottrell equation (F. G. Cottrell, Z. Physik.Chem., (1902)), Equation (1), below.

$\begin{matrix}{I = {\frac{{nFAD}^{\frac{1}{2}}}{\pi^{\frac{1}{2}}t^{\frac{1}{2}}}C}} & (1)\end{matrix}$

where

n—number of electrons per molecule of analyte

F—Faraday Constant

A—working electrode area

D—diffusion coefficient

t—time after application of potential step

C—Analyte concentration

It can be appreciated from Equation (1) that a change in the diffusioncoefficient D will lead to a change in the dose-response of the sensor.

In many electrochemical sensors, dried films of chemistry are employed,typically covering the working electrode or the working and counterelectrodes. These dried films contain enzymes that aid the exchange ofelectron(s) between the analyte and a mediator. A chemical process takesplace when a liquid sample such as blood containing the analyte ofinterest hydrates the film. During this process, the film swells,analyte molecules diffuse into the film, and, with the aid of theanalyte-specific enzymes present in the film, electron(s) are exchangedwith the mediator molecules. In the presence of a specifically appliedor controlled electrical potential, the mediator molecules diffuse tothe electrode surface and are reduced or oxidized. Resulting current isthen measured and then correlated using known techniques (e.g.amperometry, coulometry, potentiometry, voltammetry) to an amount,concentration or other desired characteristic of the analyte.

What is set forth as a simple diffusion coefficient D in Equation (1)actually (a) changes over time due to, e.g., swelling of the reagent;(b) is a sum of multiple diffusion processes (e.g., analyte diffusingfrom the fluid sample into the film to the enzyme, mediator diffusingfrom the reaction center to electrodes, etc.); and (c) may need to beadjusted to account for the kinetics of the enzyme reactions.

For the purposes of illustration, the following simple linear doseresponse equation (Equation (2)) can be used:

C=k _(BC) I _(BC) +kI _(t)   (2)

where

k_(BC), k are system specific coefficients

I_(BC) is analyte independent blank current

I_(t) is current measured at time t

Or, in terms of current densities, introducing the working electrodearea A:

C=k _(BC) Aj _(BC) +kAj _(t)   (3)

where

j_(BC)—analyte independent blank current density

j_(t)—current density at time t

In the case of a very small blank current, Equation (3) can besimplified to

C=kAj_(t)   (4)

The analyte concentration C can be inaccurately estimated by an amountΔC, which results from a change Δk that is in turn caused by, forexample, variations in composition or thickness of the chemistry filmthat occur as part of an ongoing production process. This problem ofinaccurately estimating analyte concentration can be appreciated fromEquation (5), below.

C+ΔC=(k+Δk)Aj _(t)   (5)

Since variations in composition and thickness of the chemistry film usedin these biosensors are important contributors to inaccuracy of theanalyte concentration estimation, these parameters are typicallycontrolled very well during the production process of an electrochemicalbiosensor. Nonetheless, in typical manufacturing processes, batches ofonly limited size can be produced based on, e.g., limited sized batchesof raw materials that are used to produce the final biosensor product.In many cases, a new lot of biosensors might have a significantlydifferent k, and a lot-to-lot variation as quantified in Equation (5)will thus result. Also, longer term trends, such as wear of machineparts or changes in raw material composition might also lead to a changeof k, again resulting in an incorrect slope of the dose-response curve.

A standard method known in the art to address variations in the systemspecific coefficient k is to provide a lot specific coefficient 1−Δmthat counteracts the change induced by Δk. This is represented inEquations (6) and (7), below:

C=(k+Δk)(1−Δm)Aj _(t)   (6)

With

$\begin{matrix}{{\Delta \; m} = \frac{\Delta \; k}{k + {\Delta \; k}}} & (7)\end{matrix}$

Often, pairs of lot specific coefficients are provided, a first one ofthe coefficients describing the slope, similar to 1−Δm, and the seconddescribing the intercept of a linear dose-response curve. Several lotspecific coefficients or pairs of coefficients can be stored in themeasurement instrument that is used with the biosensor and then selectedby the user or automatically selected based on information contained onthe biosensor. This approach has the drawback of requiring the meter tohave sufficient memory to store several correction coefficients and insome cases also undesirably relies upon the user to select the correctlot information. It is known that users of these devices can fail toperform such required steps.

Alternatively, another common practice known in the art involvesdownloading such correction or calibration information into the testmeter from an electronic read-only memory key (ROM key) that is insertedinto a socket of the test meter. See, e.g., U.S. Pat. No. 5,366,609.Because this calibration data may only be accurate for a particularproduction lot of test strips, however, the user is usually asked toconfirm that the lot number of the test strip currently in use matchesthe lot number for which the ROM key was programmed. This methodundesirably requires production of several different ROM keys, and alsorelies on the user to change the ROM key when using a new vial ofbiosensors, which has been found does not always occur.

Yet another known method is to provide the value of the correctioncoefficients to the measurement instrument via a code key or via thedisposable container (e.g., barcode). Another variant involves codingeach biosensor itself with a barcode or other coding information. Inthis method, when the coded biosensor is inserted into the meter, themeter automatically applies the correct correction coefficients fromseveral that are stored in its memory. While obviating the need for theuser to take any affirmative steps to ensure that the proper correctioncoefficients are being used, this method requires that the meter havestored in it all correction coefficients that correspond to the variouscodes that can be provided on multiple different lots of biosensors, andof course requires lot specific coding of the biosensors.

Still another method involves controlling the biosensor productionprocess so that only negligible lot-to-lot variations (Δk) occur, and ifneeded, those biosensors not meeting the implicit Δk≈0 requirement arerejected and discarded. This is often referred to as “universal code”.However, such methods are costly due to the large costs of meeting tighttolerances imposed in the first instance, and can be wasteful when largequantities of biosensors must be rejected and discarded for failing tomeet those tolerances. Such wastefulness can be avoided by saving thebiosensors of the rejected lots and providing them with another meterthat requires a specific code input from the user, strip or vial, i.e.non-universal code meters. However, this requires that multiple lines ofmeter products are produced and distributed, which requires additionalcosts and expenses.

Because of the large amount of waste and difficulty in meetingtolerances, the “brute force” method just discussed is largely believedby those skilled in the art to be economically unworkable on a largeproduction scale. Instead, those of skill in the art have come to acceptthe now conventional wisdom that lot to lot variations in thedose-response curve are inherent in the large-scale production ofbiosensors, and some type of calibration scheme like those discussedabove must therefore be implemented after production in order to ensurean accurate estimation of the analyte concentration in a sample.

It would be desirable to provide another method for adjusting forvariations in the dose-response curve of biosensors.

SUMMARY OF THE INVENTION

The present invention departs from the conventional wisdom noted aboveand provides a system of biosensors whose dose-response curves aremaintained within a predetermined and desired range during production byselecting a feature of the biosensors that can be varied duringproduction. Once production of these inventive biosensors is completed,calibration is unnecessary.

In one form thereof, the present invention provides a method ofmanufacturing biosensors. In this method, at least first and secondbiosensors of the same model, and typically many more, are produced. Thedose-response curve of the first biosensor is determined, typically bydosing it with a quality control solution during its manufacture andthen measuring the response. Based upon the response, a feature of thesecond biosensor, and typically many more biosensors, is determined.That feature is then implemented into production of the second andsuccessive biosensors, such that the dose-response curve of the secondand subsequent biosensors is within the predetermined range.

In one exemplary embodiment, the biosensors are electrochemicalbiosensors and the feature that is determined is the size or effectivearea of the electrical pattern of the biosensors. In this embodiment,the method involves adjusting the effective area of the electricalpattern of the second biosensor to bring the dose-response curve of thesecond biosensor within the predetermined range. For example, theelectrical pattern may comprise a working electrode having severalfingers that can be electrically disconnected during production, such asby severing the fingers with a laser, and this in turn brings thedose-response of the biosensors to within a predetermined range. Incertain embodiments, such severing effectively disconnects a portion ofthe working electrode that is exposed in the sample receiving chamber.

While the effective area of the working electrode exposed in the samplereceiving chamber is one advantageous feature that can be adjusted, anddetailed disclosures and examples of the same are provided hereinbelow,it is envisioned that one of skill in the art could employ theseteachings to determine and adjust other features of biosensors duringproduction to bring their dose response curves to within a predeterminedrange. For example, adjustment of the “excitation voltage” in anamperometric biosensor could be made by providing a resistor, current orvoltage divider in the conductive trace leading to the workingelectrode. In one form, the electrical pattern that includes theconductive trace and the working electrode may be initially formed withan ‘open’ or severed portion which, once the required dose responseadjustment is determined, can be ‘closed’ or connected with a conductivematerial known electrical characteristics that provide the desiredadjustment.

In another form thereof, the present invention provides a system ofelectrochemical biosensors comprising first and second biosensors ofgenerally the same model. The first biosensor has a first electricalpattern and the second biosensor has a second electrical pattern. Thefirst and second electrical patterns have different effective areas, andthe dose-response curves of the first and second biosensors are withinthe same predetermined range.

In this embodiment, the effective area of the electrical patterns is afeature of the biosensors that can be adjusted during production, asneeded, to maintain the dose-response of the biosensors within apredetermined range or tolerance. In one exemplary embodiment, theworking electrodes of the biosensors comprise multiple fingers. Some orall of the fingers, or portions thereof, can be electricallydisconnected to offset production variations and thus maintain thedose-response curve within a predetermined and accepted range ortolerance.

Embodiments incorporating the present invention advantageously avoid theneed for the meter and/or user to calibrate the biosensors before theuser uses them to measure analyte concentration.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned aspects of the present invention and the manner ofobtaining them will become more apparent and the invention itself willbe better understood by reference to the following description of theembodiments of the invention, taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1A is a perspective view of a biosensor formed in accordance withthese teachings;

FIG. 1B is a perspective view of a substrate of the biosensor shown inFIG. 1A having an electrical pattern formed thereon;

FIG. 2 is a fragmentary exploded perspective view of a portion of thebiosensor and substrate shown in FIGS. 1A and 1B;

FIGS. 3A-3N are fragmentary plan views of various dosing ends ofbiosensor substrates having an electrical pattern formed thereon whoseworking electrode effective area can be altered in accordance with theseteachings;

FIG. 4 is a fragmentary plan view of the dosing end of a biosensorsubstrate having an electrical pattern formed thereon whose workingelectrode effective area can be altered in accordance with theseteachings;

FIG. 5 is a perspective view shown partially schematically illustratinga production method of biosensors in accordance with these teachings;

FIGS. 6A and 6B are graphs that illustrate a method of prospectivelymaintaining the dose-response curve of biosensors within a predeterminedrange; and

FIG. 7 is a fragmentary plan view of the dosing end of a biosensorsubstrate having an electrical pattern formed thereon whose workingelectrode effective area can be sized in accordance with these teachingsto prospectively maintain the dose-response curves of the biosensorswithin a predetermined range.

Corresponding reference numerals are used to indicate correspondingparts throughout the several views.

DETAILED DESCRIPTION

The embodiments of the present invention described below are notintended to be exhaustive or to limit the invention to the precise formsdisclosed in the following detailed description. Rather, the embodimentsare chosen and described so that others skilled in the art mayappreciate and understand the principles and practices of the presentinvention.

These teachings provide a system of biosensors in which multiplesubstantially identical biosensors of the same model are provided orproduced, and in which one feature of the biosensors, such as theeffective area of the electrical pattern, is varied during production inorder to maintain the dose-response curves of all biosensors producedwithin a predetermined range or tolerance.

For purposes of this specification, the term “effective area” should beconstrued broadly, and typically refers to the size of an electricalfeature, such as an electrode, through which electricity can beconducted when the biosensor is connected to a meter or otherwiseprovided with electricity. In many cases, the effective area will besubstantially determined by the surface area of the electrical feature,which may be appropriate in the case of a substantially flat biosensorhaving a thin, flat electrical pattern formed on or in such biosensor.In other applications, effective area can be a function of whetherspecific electrical features are electrically connected to otherfeatures of the electrical pattern. Still in other applications,effective area may be a function of thickness or volume of a specificelectrical feature. In exemplary embodiments, effective area comprisesthe surface area of the working electrode that is located in the samplereceiving chamber and is also electrically connected to the meterelectronics.

The term “dose-response curve” as used herein broadly describesexperiments or testing in which fluid samples having a concentration ofa particular analyte (or multiple analytes) are deposited in or on abiosensor, and the biosensor measures a current, charge, potential,resistance, color, or some other parameter that can be correlated to theconcentration of analyte in the fluid sample. The “dose” thus refers tothe concentration of analyte and the “response” refers to the measuredparameter that corresponds to such concentration. The term“concentration-response curve” is also known in the art and issynonymous herein with “dose-response curve.”

Turning now to FIGS. 1A, 1B, and 2, there is shown one representative“model” of a biosensor 20 useful in accordance with the presentteachings, although one of skill in the art will readily recognize thatthese teachings may be incorporated into a virtually endless variety ofbiosensor models, and indeed, have applicability in other devices.Biosensor 20 includes a base substrate 22, a spacing layer 24, and acovering layer 25 comprising body cover portion 28 and chamber coverportion 30. The spacing layer 24 and the covering layer 25 cooperate todefine a sample-receiving chamber 34 extending between the basesubstrate 22 and at least the chamber cover portion 30 of the coveringlayer 25. A gap 36 is provided between body cover 28 and chamber cover30, which defines a vent opening communicating with the sample-receivingchamber 34 to allow air to escape the chamber as a sample fluid entersthe chamber from the edge opening or fluid receiving opening 45. In analternate embodiment, the covering layer could comprise a single topcover (not shown) overlying the spacing layer 24 and including a venthole (not shown) in fluid communication with the sample receivingchamber.

Biosensor 20 includes a dosing end 46 and a meter insertion end 48. Thedosing end can be configured to be distinguishable from the meter end soas to aid users. For example, dosing end 46 of biosensor 20 shown inFIG. 1 is bevelled and also is provided with a color that contrasts withthe remainder of the biosensor. Strip graphics such as arrow 41 can alsobe used to indicate the direction of insertion of the biosensor into themeter.

In one aspect of these teachings, although the effective area of theelectrical patterns or other feature may be varied on a lot to lot orother basis, the overall “look and feel” of the biosensors from eachmodel will typically be the same and indistinguishable to the user. Forexample, the strip graphics, colored dosing end, cover layer 25, spacinglayer 24, and shape and size of the biosensor would typically all beidentical or substantially identical among all biosensors of a givenmodel, even though some of the biosensors have a feature that has beenvaried during production to maintain the dose-response curve within adesired tolerance. In other embodiments, however, it may be desirable tochange certain features of individual biosensors within a particularmodel, such as color, graphics or the like. Examples of “models” ofbiosensors, as that term is used herein, include but are not limited toAccu-Chek® Comfort Curve® brand test strips or biosensors, andAccu-Chek® Aviva brand biosensors or test strips.

Turning to FIG. 1B, base substrate 22 carries an electrical pattern 50thereon having electrical features 38. Portions of the electricalfeatures 38 can also be seen in FIG. 1A in chamber 34. Electricalpattern 50 is formed on substrate 22 by, e.g., laser ablation, asdescribed in U.S. Publication No. 20050103624, the disclosure of whichis hereby incorporated herein by reference. Other suitable means forforming electrical pattern 50 include laser scribing, screen printingand other techniques known in the art. Other electrical features 38 ofelectrical pattern 50 include working electrode 52, which furthercomprises a series of fingers 54, a forked counter electrode 56, dosesufficiency electrodes 58, and a series of traces 60, 62, 64, 66, 68 and70, all of which lead from one or more respective electrical features 38to various contact pads 42 for electrical communication with a meter inwhich the biosensor is inserted. A reagent layer or film 72 is appliedat the dosing end 46 of substrate 22, and may be applied to thebiosensor by any number of methods, many of which are described inpreviously cited U.S. Publication No. 20050016844. Additional basicdesign and functional details of an electrochemical biosensor having thebasic features just noted can be found in U.S. Publication No.20050016844, the disclosure of which is hereby incorporated herein byreference.

Referring to FIG. 2, dosing end 46 of biosensor 20 is shown inperspective with spacing layer 24 and a two-piece covering layer 25exploded away. A small access opening 44 is provided through cover layer25 and spacer layer 24 and is positioned in the assembled biosensorimmediately over severed area 76 as indicated by dashed lines. Opening44 allows a laser or other tool to access a portion of some of thefingers 54 of working electrode 52 at the adjustment section 82 (FIGS.3A-3N) and sever them as shown, leaving the severed area 76, andeffectively electrically isolating or disconnecting one or more of thefingers 54, which thereby changes the effective area of the electricalpattern to a desired degree, particularly the working electrode. Asshown, e.g., three fingers 54 of the working electrode 52 are severed,leaving only two larger fingers 53, thereby reducing the effective areaof the working electrode 52 exposed within the chamber 34 by a factor ofabout 33%, assuming that fingers 53 are each individually as wide as thesum total width of all three fingers 54 combined.

The effect of adjusting the effective area of the working electrode isto maintain the dose-response within a desired tolerance. This can beunderstood from again reviewing Equation (5) that was discussed above.

C+ΔC=(k+Δk)Aj _(t)   (5)

As can be appreciated, the measured or estimated analyte concentrationis not only proportional to the constant k, but also A, which is thearea of the working electrode. Thus, a change Δk resulting from lot tolot variations can be offset by a respective change ΔA, as indicated inequation (8), below.

C=AC=(k+Δk)(A−ΔA)j _(t)   (8)

Or, expressed in terms of ΔA, Equation (9) provides:

$\begin{matrix}{{\Delta \; A} = {\frac{\Delta \; k}{k + {\Delta \; k}}A}} & (9)\end{matrix}$

Thus, by determining Δk, which can be done, e.g., by testing anindividual biosensor with a control solution of known analyteconcentration, the required change in area, if any, of the workingelectrode can be determined from equation (9). As described in furtherdetail below, this adjustment in area can be done as one of the finalsteps in a biosensor manufacturing process, or it can be done on aprospective basis and incorporated into an earlier stage of theproduction process during which the electrical patterns are formed onthe substrates.

If the effective area of the electrical pattern of the biosensor is tobe adjusted during a later production stage, e.g., after the biosensorsare already essentially formed, the system in accordance with theseteachings may provide various options for making the adjustment.

As alluded above, in certain exemplary embodiments, the “effective area”to be adjusted comprises the surface area of the working electrode thatis located in the sample receiving chamber. In these embodiments, toprovide the range of adjustability with respect to the dose responsecurve, the working electrode may typically be provided with a basicportion that is the same in all biosensors of a given model. The workingelectrode may also include several other fingers that can be selectivelysevered to alter the dose response curve.

For example, FIGS. 3A and 3B depict an exemplary embodiment of a dosingend 46 of a substrate 22 suitable for use in the system of biosensors inaccordance with these teachings. (Dosing end 46 is also shown in FIGS. 1and 2.) An electrical pattern 50 is provided having a working electrode52 that further comprises a series of adjustment fingers 54, permanentfingers 53 that are wider than fingers 54, a counter electrode 56, anddose sufficiency electrodes 58. The capillary space or sample receivingchamber is shown at reference numeral 55 as a dashed line, and a reagentfilm or layer (not shown in FIGS. 3A-3N) is typically present in atleast a portion of this capillary space at least in contact with theworking electrode 52, as discussed above with reference to FIGS. 1 and2.

In this exemplary embodiment, permanent fingers 53 of working electrode52 provide approximately 80% of the nominal value of the area of theworking electrode that is located in the sample receiving chamber. Bycontrast, fingers 54 of working electrode 52, which extend into thecapillary and are selectively severable, provide an additionalapproximately 40% of the nominal value. As a result, in this particularembodiment, the dose response curve can be adjusted between up to about120% of the nominal working electrode area (all fingers 54 unsevered) ordown to 80% (all fingers 54 completely severed). Of course, one of skillin the art would readily recognize that the percentages just noted canbe varied as desired by, e.g., providing fingers 53 and/or 54 wider ornarrower, and/or providing more of less than the three selectivelyseverable fingers 54. A working electrode effective area that may bevaried between about 80% to 120% of its nominal value during productionis merely one exemplary range believed sufficient to maintain the doseresponse curve within a desired range for certain methods of massproducing the inventive biosensors. One of skill in the art may wish towiden or narrow this range, depending upon the variations in doseresponse curve encountered in the particular manufacturing method inwhich these teachings are employed.

FIG. 3A illustrates the electrical pattern as it is initially formed onsubstrate 22, such as by laser ablation or other suitable means, asdescribed above, whereas FIG. 3B shows the electrical pattern 50 afterthe adjustment to the area has been made. More specifically, theadjustment section 82 shown projected over a portion of adjustmentfingers 54 in FIG. 3A represents a location where one or more of theadjustment fingers 54 can be severed, e.g., during a final stage ofproduction. FIG. 3B shows the electrical pattern after three fingers 54have been severed, in which a severed area 76 is formed where conductivematerial was removed. Thus, the effective area of the working electrodein this case has been reduced from about 120% of its nominal value toabout 80% of its nominal value, since the sections of the three fingers54 that extend upwardly and between the counter electrode have beenelectrically disconnected.

An access opening such as opening 44 shown in FIGS. 1 and 2 is providedin the covering layers directly over the adjustment section 82 so thatthe severing of fingers 54 as depicted in FIGS. 3A and 3B can beperformed in a later stage of production. As just alluded, and asexplained in further detail below, the number of adjustment fingers 54that are to be severed, if any, is a design choice based upon themagnitude of the correction desired to be made to the dose-responsecurve of the particular biosensors being produced.

The embodiment shown in FIGS. 2 and 3A and 3B has certain advantages inthat the wider fingers 53 are generally more robust than thinnerfingers. Further, in this case, since fingers 53 define the outer edgesof the working electrode, the gap widths between the top and bottomedges of the working electrode and the corresponding edges of thecounter electrode remain the same irrespective of the number of fingers,if any, that are to be severed. This may be desirable in certaincircumstances, as described below.

FIGS. 3C and 3D illustrate an alternate embodiment which differs fromthat of FIGS. 3A and 3B, in that the working electrode 157 includes onlya single wider permanent finger 153 and three smaller fingers 154 thatare selectively severable. In this case, the area of finger 153 maycomprise, e.g., about 80% of the nominal value, whereas three fingers154 combined may comprise an additional 40% of the nominal workingelectrode area. As with the embodiment shown in FIGS. 2, 3A and 3B, thegap width between the edges of the counter and working electrodesremains the same irrespective of the number of fingers, if any, that areto be severed. FIG. 3D illustrate all three fingers 154 being severed atsevered area 76.

The working electrode of the embodiment shown in FIGS. 3E and 3F issomewhat the inverse of that shown in FIGS. 3A and 3B. In this case,there is a single wider permanent finger 53 centered between two sets ofthree smaller selectively severable fingers 54. This embodiment allowsgreater precision in adjustment due to there being two adjustmentsections 82 and 82 a, each of which allows severing zero to threefingers 54. FIG. 3F shows two severed areas 76 and 76 a.

In FIGS. 3G and 3H, two sets of adjustment fingers 154 and 156 areprovided in addition to permanent fingers 153. The fingers 154, 156 areseparated by a space 150 therebetween. In addition to a first adjustmentsection 82 for severing fingers 154, a second adjustment section 84shown in dashed lines in FIG. 3G is accessible by a cutting apparatussuch as a laser. FIG. 3H illustrates an adjustment in which alladjustment fingers 154 and 156 have been severed, leaving severed areas76, 86, but this of course need not be the case. Any number andcombination of fingers 154 and 156 or none at all may be severed,depending upon the precise correction desired to be made to thedose-response curve.

FIGS. 3I and 3J illustrate another alternate embodiment in which theworking electrode 157 is formed differently than working electrode 152shown in FIGS. 3G and 3H. It has a connecting band 151 of conductivematerial disposed centrally with respect to the capillary channel 55 asillustrated. Two adjustment sections 82 and 84 are shown in FIG. 3I, andall selectively severable fingers are shown severed in severed areas 76and 86 shown in FIG. 3J.

FIGS. 3K and 3L illustrate yet another embodiment of a dosing end 46 ofa substrate 22 suitable for use in the system of biosensors inaccordance with these teachings. In this case, working electrode 52comprises a series of adjustment fingers 54, permanent fingers 53, acounter electrode 56, and dose sufficiency electrodes 58. One adjustmentarea 82 is provided as shown in FIG. 3K, and all fingers 54 are shown asbeing severed in severed area 76 shown in FIG. 3L.

In addition to removing material or severing it to reduce the effectivearea of the electrical pattern, conductive material may be instead addedto an electrical pattern during biosensor production to electricallyconnect conductive material and thus increase the size of the effectivearea of the electrical pattern. For example, FIGS. 3M and 3N illustratean embodiment in which the electrical pattern 50 is similar to thatshown in FIGS. 3K and 3L, except that the electrical pattern 50 isinitially formed with a severed area 76 (FIG. 3M), and during, e.g., afinal stage of production, conductive material 90 is deposited throughan access opening or window (such as opening 44 shown in FIGS. 1 and 2)and connects the fingers 54 as illustrated in FIG. 3N. The conductivematerial 90 may be deposited by any of a wide variety of methods knownin the art. As another variation, a “plug” of conductive material may beprovided in an access opening window such as opening 44 (FIG. 1) in africtional fit and spaced away from the electrical pattern and substrate22. This plug could then be tapped downward if desired during productionto contact and thus electronically connect fingers 54. One of skill inthe art would readily recognize any number of switching mechanisms thatcould be provided and activated during the production process to connectone or more adjustment fingers 54 as desired to adjust the effectivearea of the electrical pattern.

Having set forth general examples of how the effective area of theelectrical pattern may be varied, a more detailed example with numericalvalues is provided with respect to FIG. 4, which illustrates a dosingend 246 of a substrate 222 suitable for use in the system of biosensorsin accordance with these teachings. An electrical pattern 250 isprovided having a working electrode 252 that includes two multi-fingeredsections 254 and 256. Section 254 includes permanent fingers 262 andadjustment fingers 264. Similarly, section 256 includes permanentfingers 266 and adjustment fingers 268. All adjustment fingers 264 and268 are connected to the center part 272 of the working electrode 252 bymeans of the permanent fingers. A reagent film 274 (represented as a dotmatrix) extends across the dosing end 246 of substrate 222, coveringmost of the counter electrode and working electrode. A counter electrode270 and dose sufficiency electrodes 280 are also provided as shown, anda capillary boundary is shown in dashed lines as indicated by referencenumeral 255. Of course, traces or leads extend from the working,counter, and dose sufficiency electrodes and terminate in contact padsthat connect to a meter, as described above and shown in FIGS. 1A and1B.

FIG. 4 also shows in dashed lines two adjustment windows 284 and 286which represent windows such as access opening 44 (FIG. 1) through whichthe adjustment traces 264 and 268 could be accessed and severed ifdesired during production. Also, although the embodiment shown in FIG. 4contemplates four permanent fingers, two each of fingers 262 and 268, asingle permanent finger would be sufficient to ensure the basic functionof the biosensor. However, in other cases it may be desirable tomaintain a constant gap width between counter electrode 270 and workingelectrode 252 over the full width of the capillary channel, such as,e.g., if impedance measurements are used to correct for hematocrit ortemperature, as is done in some biosensors that estimate glucoseconcentration in whole blood. See, e.g., U.S. Pat. No. 6,645,368, andU.S. Patent Application Serial Nos. 2004-0157337, 2004-0157338 and2004-0157339. Permanent fingers 262 and 266 define the top edge of theworking electrode as shown in FIG. 4 and accomplish the objective ofmaintaining constant gap width over the width of the capillary channel,if desired.

As also can be appreciated from FIG. 4, the adjustment windows 284 and286 are located below and spaced away from the reagent film, whichallows easier and more accurate severing of fingers 264 and 268, sincethey are not covered by the reagent film in the location shown and thelatter thus does not interfere with cutting the fingers. Further, it maybe desirable when, e.g., employing a laser to sever the fingers, toavoid illuminating the reagent since the laser light may undesirablyaffect the reagent chemistry. It is nonetheless possible to position thewindows over the reagent film if desired in certain applications.

Table 1, below, provides examples of actual dimensions that areconsistent with the formation of the electrical pattern shown in FIG. 4by, e.g., a laser ablation process. As indicated by the examples, theoverall length of the main working electrode area 272 across thecapillary space 255 (e.g., from left to right in FIG. 4) is 1.15 mm andits overall width in the capillary space is 0.29 mm. The permanentfingers 262 and 268 are represented in Table 1 as two fingers with awidth of 0.04 mm and a length of 0.35 mm located within the capillaryand close to each side of the capillary boundary. There are six (6)adjustment fingers (three each of fingers 264 and 268) that are allrepresented the same in Table 1 since they are all substantially thesame width and length.

The fifth column of Table 1 shows the sum total working electrode area,which increases proceeding down the column. For example, the totalworking electrode area attributed to area 272, and permanent fingers 262and 266 is 0.362 mm². Adding only one adjustment finger increases thearea to 0.365 mm², whereas adding all six adjustment fingers brings thetotal area to 0.384 mm², as indicated in Table 1.

Table 1 is presented such that a configuration of electrical pattern 250of FIG. 4 having three adjustment fingers (264 or 268) connected and theother three adjustment fingers severed or disconnected is established asa baseline nominal working electrode area of 100.0%. Thus, cutting allsix fingers provides 97% of the nominal area and cutting none of thefingers provides 103% of the nominal area, as indicated. From equation(9), the resulting set of ΔA's are {−0.037, −0.024, −0.012, +0.012,+0.024, +0/037}.

TABLE 1 Width* Length* Finger Area ΣWE area Effective Area ElectricalFeature (mm) (mm) (mm²) (mm²) Adjustment Main working electrode (WE)0.29 1.15 0.33350 WE permanent finger 1 0.04 0.35 0.01400 WE permanentfinger 2 0.04 0.35 0.01400 0.362 97.0% WE adjustment finger 1 0.03 0.1250.00375 0.365 98.0% WE adjustment finger 2 0.03 0.125 0.00375 0.36999.0% WE adjustment finger 3 0.03 0.125 0.00375 0.373 100.0% WEadjustment finger 4 0.03 0.125 0.00375 0.377 101.0% WE adjustment finger5 0.03 0.125 0.00375 0.380 102.0% WE adjustment finger 6 0.03 0.1250.00375 0.384 103.0% *in capillary space

Table 1 illustrates adjusting the effective area in 1% increments.However, in another embodiment, the working electrode effective areacould be provided in increments of −9%, −6%, −3%, nominal, +3%, +6% and+9% by the adjustment finger arrangement just noted or other adjustmentarrangements disclosed above. One of skill in the art could provideother increments and combinations thereof to meet the system drift thatis contemplated or encountered in a particular manufacturing process.

Turning now to FIG. 5, an exemplary method of manufacturing biosensorsin accordance with these teachings is illustrated. A first line orproduction station of biosensors 300 includes a roll 301 of biosensors20 provided in a reel to be unwound as indicated. Biosensors 20 on roll301 are substantially as described above with reference to FIGS. 1 and2, except the biosensors are provided in a continuous web and have notyet been trimmed and cut into individual biosensors, which occurs as afinal stage of production. As roll 301 is unwound, a dispenser 302containing aqueous quality control (“QC”) solution 304, e.g., acalibrator solution, doses selected ones of the biosensors 20 with QCsolution 304. As shown, the QC solution is drawn into the samplereceiving chamber of the selected biosensor.

In the process illustrated in FIG. 5, the roll may stop momentarilywhile dispenser 302 quickly doses the biosensor, or the roll may movecontinuously. As the selected biosensor 20 moves, the chemical andphysical processes quickly take place in chamber 34. The selectedbiosensor 20 is advanced to a testing station 306 and then contacted byprobes 308, which are shown in FIG. 5 contacting a biosensor 20 that isshown located in FIG. 5 three biosensors ahead of the selected biosensorin the line. A meter or measurement device 309 having an optionaldisplay 311 provides an excitation sequence to the selected biosensors20 through probes 308 and records the response signal. Computing device313 receives and records the response for all biosensors that are testedin a roll or multiple rolls and calculates the desired correction to bemade in the effective area of the electrical patterns.

Positioned three biosensors ahead of the testing station 306 in line 300is a wicking station 310 which can reciprocate as depicted by an arrowand includes a wick element 312 that contacts the dosing end of theselected biosensor and draws the QC solution 304 therefrom.

Finally, positioned another four biosensors forward in the line is areciprocably mounted marking station 314 having a marker or stamp 316shown in the shape of an “X” that imprints a reject mark 318 on thosebiosensors that have been selected for testing. Reject mark 318 is shownin phantom in line 300 since the biosensor shown positioned understation 314 has not been dosed and therefore would not actually bemarked with an “X.” The ratio of biosensors tested to total produced inthe production line is a design variable, but it is envisioned that manymay be tested. In one embodiment of this design variable, an entire vialof 50 strips is tested periodically during production. For example, in areel-to-reel based manufacturing process such as is employed in makingACCU-CHEK® Aviva test strips, there are typically about 111 strips permeter, and 50 strips are selected for testing about every 200 meters.Thus, the ratio is about 1 strip selected for testing per every 445strips that are produced. The optimum ratio depends in many respectsupon the reproducibility of each lot of reagent produced as well as thereproducibility of applying the reagent layer film on the dosing end 46of substrate 22. The greater the combined reproducibility, the higherthe ratio of tested strips to strips produced. Although the testing isdestructive, the small ratio of tested biosensors that are discarded pertotal produced does not significantly increase production costs, and isindeed more than offset by obviating prior art solutions such asproviding ROM keys, bar codes and the like.

With further reference to FIG. 5, after selected ones of the biosensors20 are dosed, tested, wicked and marked, they are wound up in a secondroll 322 to be further processed in line 330. Line or station 330includes a camera 332, a laser 334 and an optical arrangement shownschematically with a mirror 336. Laser 334 has a computer orcomputing/machine control system 338 associated therewith that receivesthe calculated area correction of, e.g., the working electrodes of theelectrical patterns, from the first computer 313.

Camera 332 is used in conjunction with system 338 to allow the laser tocut as required to adjust the area of the working electrode of allbiosensors in line 330. More particularly, as line 330 advancesbiosensors 20 from left to right as illustrated, laser 334 pulses beams340 that are reflected by mirror 336 and projected through windows oraccess openings 44 and, e.g., makes a cut like that described withreference to FIGS. 3A and 3B, above, to produce severed area 76 asneeded. The optical result read by the camera is processed by thecomputing system 338 to ensure that the laser is properly making therequired cuts in the area designated. After this adjustment is made, thebiosensors are rewound onto roll 342 for further processing, duringwhich the biosensors are, e.g., separated from the roll, trimmed andpackaged in vials. Details of the further processing of the type justnoted to complete strip assembly are provided in U.S. Publication No.20050013731, the entire disclosure of which is incorporated herein byreference.

While one method of production is illustrated in FIG. 5, one of skill inthe art would readily recognize many variations. For example, while twoseparate stations 300 and 330 are shown in FIG. 5, the functions ofthese two stations could feasibly be combined in a single, albeit longerline. In other words, line 300 could be lengthened and laser 334 andcamera 332 could be positioned downstream of the marking station 314 inthis single line. Furthermore, line 300 depicts the dosing, testing,wicking and marking stations spaced apart along the line such that theline can continually move while selected biosensors are tested. However,if desired, these stations could be positioned all together and the linecould be periodically stopped when one of the biosensors is to betested. When only few of the biosensors are to be tested, this optionmay be more desirable in terms of setting up the line. Furthermore, theline could be stopped and the testing could be done manually by, e.g., atechnician trained for such purpose. One of skill in the art wouldrecognize various other options for incorporating these teachings intothe production of biosensors.

A second aspect of these teachings enables the biosensors to be adjustedfor an accurate estimation of analyte concentration by prospectivelypredicting using statistical process control (SPC) the adjustment neededof the area of the electrical pattern of biosensors that have not yetbeen produced. To illustrate this inventive aspect, FIG. 6A shows anaverage biosensor response to an aqueous control solution per lot(referred to as “homogeneity lot mean”) for several production lots.Homogeneity lot mean is determined by a protocol that involvesstatistical sampling of biosensors from multiple rolls that form theproduction lot. Also shown in FIG. 6A are release limits above and belowwhich a lot is typically discarded as insufficient even for use insystems employing complex correction algorithms. Also shown aretheoretical control limits and center lines, the theoretical controllimits representing the predetermined range or tolerance within whichthe response of the biosensors is desired to be maintained. The runningaverage is plotted as a solid black line.

As can be appreciated from the illustrated results in FIG. 6A, theaverage homogeneity lot mean (solid line) dips below the lower controllimit starting with approximately lot 102, and then crosses over andbelow the lower control limit six (6) more times before finally crossingthe upper control limit at about lot 540. These trends can be monitoredand prospective corrections can be implemented with SPC.

Specifically, FIG. 6B shows the expected homogeneity lot means if aworking electrode area correction made in accordance with the aboveteachings were to be employed. The nominal (no correction) workingelectrode area A₀ is used for all lots up to lot 102. At this point, asdiscussed above, the lower threshold is crossed and the workingelectrode area for subsequent lots is then adjusted to (A₀+2%) asindicated in FIG. 6B. As can be appreciated, by maintaining the workingelectrode area at a value of (A₀+2%), the homogeneity lot mean shown inthe solid line is maintained between the upper and lower control limitsfor hundreds of subsequent lots, which was not the case depicted in FIG.6A without the area adjustment. At lot 472, the upper SPC control limitis crossed. To compensate for this, biosensors of subsequent lots havetheir working electrode areas brought back to A₀. After the upper SPCcontrol limit is crossed again at lot 540, the working electrode area ofthe biosensors is changed to (A₀−2%) as indicated in FIG. 6B.

As alluded above, since the correction is prospective, it can be builtinto an earlier stage of the manufacturing process of the biosensors, ifdesired, which may offer certain advantages in terms of economies ofproduction and ease of implementation. FIG. 7 illustrates a dosing end446 of a substrate 422 suitable for employing the prospectivecorrections described with reference to FIG. 6B. An electrical pattern450 is provided having a working electrode 452, a counter electrode 456having two fingers or segments 458 and 460, and dose sufficiencyelectrodes 462. The electrical pattern 450 can be formed from laserablation, laser scribing, screen printing or other known techniquesknown in the art to produce electrical patterns on a biosensorsubstrate(s). The capillary space or sample receiving chamber 434 isdelineated by boundary 436 shown as a dashed line. A reagent film orlayer 464 covers the electrodes.

The working electrode 452 has a width “W” as indicated, whereas the gapsbetween working electrode 452 and segments 458 and 460 are denoted G₁and G₂, respectively. Tables 2, 3 and 4 illustrate three differentoptions for adjusting the area of the working electrode in combinationwith various gap width changes.

Table 2, below, illustrates an option in which gaps G₁ and G₂ aremaintained while the width W of working electrode 452 is varied.

TABLE 2 WE area, mm² Δ WE area W (mm) G₁ (mm) G₂ (mm) 0.390 +4% 0.2600.255 0.255 0.383 +2 0.255 0.255 0.255 0.375  0% 0.250 0.255 0.255 0.368−2% 0.245 0.255 0.255 0.360 −4% 0.240 0.255 0.255

Table 3 provides an option in which the width W of the working electrodeas well the gap G₂ between working electrode 452 and segment 460 of thecounter electrode are varied. By contrast G₁ is maintained constant,which may have certain advantages in terms of reliably and reproduciblydetecting sample entering the sample receiving chamber 434.

TABLE 3 WE area, mm² Δ WE area W (mm) G₁ (mm) G₂ (mm) 0.390 +4% 0.2600.255 0.245 0.383 +2 0.255 0.255 0.250 0.375  0% 0.250 0.255 0.255 0.368−2% 0.245 0.255 0.260 0.360 −4% 0.240 0.255 0.265

Table 4, below, illustrates an option in which the working electrodewidth W and the gaps G₁ and G₂ are varied symmetrically, which maintainsa constant measurement volume, which may have certain advantages whenusing these teachings for, e.g., coulometric measurements.

TABLE 4 WE area, mm² Δ WE area W (mm) G₁ (mm) G₂ (mm) 0.390 +4% 0.2650.250 0.250 0.383 +2 0.260 0.252 0.252 0.375  0% 0.255 0.255 0.255 0.368−2% 0.250 0.258 0.258 0.360 −4% 0.245 0.260 0.260

While exemplary embodiments incorporating the principles of the presentinvention have been disclosed hereinabove, the present invention is notlimited to the disclosed embodiments. Instead, this application isintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims.

1-34. (canceled)
 35. A system of electrochemical biosensors, comprising:first and second biosensors of the same model, the first biosensorhaving a first electrical pattern including a first plurality ofadjustment fingers and the second biosensor having a second electricalpattern including a second plurality of adjustment fingers; the firstand second electrical patterns having different numbers of theirrespective adjustment fingers electrically disconnected and therebyhaving different effective areas; and wherein the dose-response curvesof the first and second biosensors are within a common predeterminedrange.
 36. The system of claim 35, wherein the first and secondelectrical patterns each comprise working and counter electrodes,wherein the working electrode of the first electrical pattern has aneffective area that is different than the effective area of the workingelectrode of the second electrical pattern.
 37. The system of claim 36,wherein the working electrodes of the first and second electricalpatterns comprise the first and second pluralities of adjustmentfingers, respectively, at least one of the fingers of the firstelectrical pattern being electrically disconnected.
 38. The system ofclaim 37, wherein a reagent covers a portion of the working electrodesand the at least one finger is severed in a location spaced from theportion of the working electrodes that is covered by the reagent. 39.The system of claim 35, wherein the first and second biosensors eachcomprise: a substrate, the substrate of the first biosensor having thefirst electrical pattern formed thereon and the substrate of the secondbiosensor having the second electrical pattern formed thereon, the firstand second electrical patterns each comprising a working electrode, acounter electrode and contacts configured to connect the biosensors to ameter; one or more of a spacing layer and a covering layer overlying thesubstrate and cooperating with the substrate to define a samplereceiving chamber; and a reagent disposed in the sample receivingchamber and contacting at least a portion of the working electrode. 40.The system of claim 39, wherein the substrate, the one or more of aspacing layer and a covering layer, and the reagent are allsubstantially identical in the first and second biosensors.
 41. Thesystem of claim 39, wherein the one or more of the spacing layer andcovering layer comprise an opening through which a section of the firstand second electrical patterns can be accessed during production. 42.The system of claim 35, further comprising a third biosensor having athird electrical pattern, the first and third electrical patterns beingidentical, wherein the dose-response curves of the first, second andthird biosensors are within the same predetermined range.
 43. The systemof claim 35, further comprising a third biosensor having a thirdelectrical pattern having a third plurality of adjustment fingers, thefirst, second and third pluralities of fingers each comprising adifferent number of electrically disconnected fingers, wherein thedose-response curves of the first, second and third biosensors arewithin the same predetermined range.
 44. The system of claim 35, whereinthe first biosensor and the second biosensor are produced in differentproduction lots.
 45. The system of claim 35, wherein the first biosensorand the second biosensor are produced in the same production lot.
 46. Amethod of manufacturing electrochemical biosensors of the same model,the biosensors each having an electrical pattern comprising severaladjustment fingers which can be individually disconnected from orconnected to the electrical pattern to adjust the effective area of theelectrical pattern, the method comprising: (a) producing first andsecond biosensors; (b) determining the dose-response curve of the firstbiosensor; (c) selecting the effective area of the electrical pattern ofthe second biosensor as a function of the dose-response curve of thefirst biosensor; and (d) connecting or disconnecting at least one of theseveral adjustment fingers of the second biosensor to achieve theselected effective area, wherein the dose-response curve of the secondbiosensor falls within a desired predetermined range.
 47. The method ofclaim 46, wherein the first and second biosensors are produced in thesame production lot.
 48. The method of claim 46, further comprising rollto roll processing, wherein the first and second biosensors are locatedon different rolls during production.
 49. The method of claim 46,wherein the first and second biosensors are produced in differentproduction lots.
 50. The method of claim 46, wherein step (d) compriseselectrically disconnecting at least one of the several adjustmentfingers in the second biosensor.
 51. The method of claim 50, wherein theelectrically disconnected adjustment finger comprises a segment of aworking electrode.
 52. The method of claim 51, wherein the electricallydisconnected adjustment finger is positioned at least partially within acapillary chamber of the second biosensor.
 53. The method of claim 46,wherein the adjustment fingers extend into a capillary chamber.
 54. Themethod of claim 46, wherein step (b) is performed before the electricalpattern is formed on the second biosensor.
 55. The method of claim 46,further comprising: providing the electrical pattern of the secondbiosensor on a substrate; and laminating at least one covering layer ora spacing layer over the substrate, thereby forming a cover and a samplereceiving chamber on the second biosensor.
 56. The method of claim 55,wherein step (d) comprises penetrating the at least one covering layeror a spacing layer to sever the at least one of the several adjustmentfingers of the electrical pattern of the second biosensor.
 57. Themethod of claim 56, wherein the severing is performed with a laser. 58.The method of claim 46, wherein step (b) comprises destructive testingof the first biosensor.
 59. A method of manufacturing electrochemicalbiosensors of the same model, comprising: (a) producing a firstbiosensor having a first electrical pattern with a first effective area;(b) determining a dose-response curve of the first biosensor; (c) usingthe dose-response curve determined for the first biosensor to determinea second effective area for a second electrical pattern of a secondbiosensor, the second effective area being different from the firsteffective area; and (d) forming the second biosensor, the secondeffective area being obtained during formation of the second electricalpattern, wherein the second biosensor has a dose-response curve that iswithin a desired predetermined range.
 60. The method of claim 59,wherein step (a) comprises forming a first working electrode of thefirst biosensor with a first width and step (d) comprises forming asecond working electrode of the second biosensor with a second widththat is different from the first width.
 61. The method of claim 60,wherein step (a) comprises forming the first working electrode and afirst counter electrode with a gap therebetween and step (d) comprisesmaintaining the same size of the gap in the second biosensor.
 62. Themethod of claim 60, wherein step (a) comprises forming the first workingelectrode and a first counter electrode with a first gap therebetweenand step (d) comprises forming the second working electrode and a secondcounter electrode with a second gap therebetween, the second gap havinga different size than the first gap.
 63. The method of claim 59,wherein: the first biosensor comprises a plurality of first biosensors;the dose-response curve determined in step (b) comprises an averagedose-response curve of the plurality of first biosensors; and the secondbiosensor comprises a plurality of second biosensors.
 64. The method ofclaim 63, further comprising: determining an average dose-response curveof the plurality of second biosensors; determining a third effectivearea for a third electrical pattern for a plurality of third biosensors,the third effective area being different from the second effective area;and forming the plurality of third biosensors with the third electricalpatterns having the third effective area, wherein the plurality of thirdbiosensors has a dose-response curve that is within the desiredpredetermined range.
 65. The method of claim 64, wherein the first andthird effective areas are the same.
 66. The method of claim 63, whereinthe plurality of first biosensors comprises a first production lot ofbiosensors and the plurality of second biosensors comprises a secondproduction lot of biosensors.
 67. The method of claim 63, furthercomprising establishing upper and lower control limits which define thedesired predetermined range.